A membrane separation technique has been hitherto used for seawater desalination, water purification treatment, gas separation, hemocatharsis and the like, in which researches have been recently advanced to apply the membrane separation technique to waste water treatment from the viewpoint of environmental protection.
Hitherto, sand filtration, gravity sedimentation and the like have been carried out as processes for accomplishing solid-liquid separation of treated water high in turbidity, such as water purification treatment, sewage, waste water treatment, treatment of industrial waste and water and the like. However, the solid-liquid separation by these processes have problems such as occurrence of a case where the water quality of obtained treated water becomes insufficient or of requiring a vast site for the solid-liquid separation.
As processes for solving these problems, a variety of studies have been made in recent years on a process for accomplishing the solid-liquid separation of treated water by using a membrane module provided with a separation membrane such as a precision filtration membrane, an ultrafiltration membrane or the like. With these processes, the filtration treatment for treated water is carried out by using a separation membrane, and therefore treated water high in water quality can be obtained (see, for example, Non-patent Citation 1).
In case of accomplishing the solid-liquid separation of treated water by using a separation membrane, clogging at a separation membrane surface with suspended matter proceeds with continuation of filtration treatment, thereby resulting in lowering in filtration flow amount or rising of a differential pressure across the membrane. In order to restore such a condition, a diffuser pipe is disposed below the membrane module to accomplish a process for peeling off the suspended matter at the separation membrane surface by swingingly move the treated water at the membrane surface under the action of air diffused from this diffuser pipe. (see, for example, Patent Citations 1 and 2).